1. Field of the Invention
The present invention relates to a ceramic electronic component, and more specifically, an electric component for a positive temperature coefficient thermistor (PTC thermistor) and the like comprising a ceramic, such as a semiconductive ceramic mainly containing barium titanate.
2. Description of the Related Art
Barium titanate semiconductive ceramics have been used for PTC thermistors which are generally used for the demagnetization of cathode-ray tubes, overcurrent protection, and other things. Lowering the resistance of the barium titanate semiconductive ceramics leads to a miniaturized and heavy-current ceramic electronic component, and accordingly, a laminated ceramic electronic component having inner electrodes has been developed.
As technology has progressed, higher reliability for the ceramic electronic component has been demanded. In order to maintain moisture, heat or weather resistance of the ceramic electronic component, the surface thereof is conventionally coated with an organic resin or an inorganic glass to form a protective layer, thereby preventing the degradation of the reliability. In particular, a ceramic electronic component has been improved in reliability, for example, by using materials having a small difference of the thermal expansion coefficients between the component and the protective layer thereof as disclosed in Japanese patent publication No. 3-79842.
However, electrodes of a known laminated-ceramic electronic component have to use a base metal such as Ni to ensure ohmic contact, and therefor the component has to be burned in a reducing atmosphere.
Furthermore, the protective layer of the ceramic electronic component formed by coating an organic resin or an inorganic glass is deteriorated by heat generated by being applied in packaging or generated by surrounding electronic components after board level packaging. Such a protective layer cannot be used for a long time even though the difference of the thermal expansion coefficients between the component and the protective layer thereof is small.
On the other hand, the PTC characteristic of barium titanate semiconductors is lowered by burning in a reducing atmosphere, and consequently the withstand voltage is lowered.